Not applicable.
Power is conventionally transmitted from the engine of an automobile or a truck through one of two conventional combinations of power transmission devices. One combination is a mechanically operated friction clutch and a manually shifted countershaft transmission. The other combination is a hydrodynamic drive, typically a torque converter, and an automatically shifted planetary gear transmission.
The clutch and manually shifted countershaft transmission combination includes a friction clutch that is mounted to a flywheel on the vehicle""s engine. An input shaft of the countershaft transmission engages and is driven by a driven component of the clutch, conventionally a disk that frictionally engages the flywheel. Countershaft transmissions have meshing gears mounted on parallel shafts. The speed ratio and torque ratio provided by the transmission depends on the ratios of the meshing pairs of gears through which power is transmitted from the input shaft of the transmission to the output shaft. A countershaft transmission is conventionally either a sliding gear transmission or a constant mesh transmission. In a sliding gear transmission, gears are moved along a shaft into or out of engagement with another gear to change the path through which power is transmitted through the transmission and thereby changes the transmission ratios. In a constant mesh transmission, gears are constantly in mesh and positive engagement or friction devices couple the gears to a shaft of the transmission. In either type of transmission, ratios are changed by operation of a shifter mechanism that moves gears in the case of a sliding gear transmission or operates friction or positive engagement devices in the case of a constant mesh transmission.
The hydrodynamic drive and automatically shifted planetary gear transmission combination is driven by a torque converter mounted to a flywheel on an engine. An input shaft of a planetary gear transmission engages and is driven by the torque converter. The planetary gear transmission conventionally has planetary gear assemblies aligned along the axis of the input shaft. Power is transmitted through the planetary gear assemblies by fixing one of the three components of the assembly, the sun gear, the plane gear carrier, or the ring gear, against rotation and applying power to one of the other two components to drive the remaining component. The drive ratio of the transmission is determined by the diameters of the gears of the planetary gear assemblies through which power is transmitted. The path through which power is transmitted through planetary gear assemblies is changed by hydraulically operated devices. A hydraulically operated brake having a band that is mounted to the transmission case and surrounds the ring gear of a planetary gear assembly is conventionally used to secure the ring gear to the transmission case. When the ring gear is secured to the transmission case, power may be transmitted through the sun and planet gear carrier of the planetary gear assembly. Hydraulically operated clutch pack assemblies having adjacent disks that alternately engage a surrounding case and an inner splined shaft are used to selectively couple and uncouple the shaft to the case by applying or removing a hydraulic pressure to the assembly. Hydraulically operated frictional engagement devices, brake bands and clutch packs, provide control of the performance of the transmission. Frictional engagement devices that engage and disengage to change the ratio of planetary gear transmissions can provide a high level of mechanical reliability. Because those devices are actuated by hydraulic pressure, planetary gear transmissions are conventionally shifted automatically by controlled application of hydraulic pressure to frictional engagement devices in the transmission.
These conventional power transmitting combinations have been the bases from which power transmitting combinations and devices have been specifically designed and constructed for use in racing. Racing that primarily requires acceleration, in particular, requires transmissions that are more durable and that must satisfy different requirements than do conventional automotive transmissions. In acceleration racing, such as drag racing, either the maximum available power or the maximum power that can be used to accelerate the car is transmitted through the driveline of the racecar throughout the race. The transmission must provide a high degree of mechanical reliability both in changing gear ratios and in structural reliability. Failure to quickly change gears and failure of a component of the transmission are both causes of lost races.
Cars having the most powerful engines used in drag racing have long required transmissions specifically constructed to transmit the large power created by their engines. Specially constructed planetary gear transmissions that have large and high strength gears and other components have been used in various forms of racing, including drag racing for many years. These transmissions, manufactured by Lenco, Inc. and others, have used high strength planetary gear assemblies with mechanically operated friction engagement devices to provide both reliable changes of transmission ratios and structural reliability.
The most powerful cars for which planetary gear transmissions were specially constructed have conventionally driven these transmissions by clutches that are constructed to provide a significant amount of control of the rate at which the high power generated by the engines of these cars is applied to the driveline of the racecar. The planetary gear transmissions specially constructed for racing and used in the most powerful racecars are coupled to the engine differently than planetary gear transmissions used in conventional automotive applications in that they have been driven by clutches and have conventionally been shifted by mechanically or pneumatically, rather than hydraulically, actuated mechanisms.
While racing planetary gear transmissions provide mechanically reliable gear ratio changes and structural reliability, that reliability comes at the price of requiring power to drive the large and heavy components of the transmission. A significant amount of power is required to drive heavy components of racing planetary gear transmissions. The power required to drive racing planetary gear transmissions is not a significant disadvantage to racecars having the highest power engines. However, the power required to drive these transmissions is a significant disadvantage to racecars that are limited to engines that do not produce more power than the racecar can utilize to increase performance. For such cars, decreasing the power consumed by driving components of the car increases the power that can be used to drive the car and to thereby increase performance.
Countershaft racing transmissions that require less power to drive than racing planetary gear transmissions have recently been developed. In addition to requiring less power to drive than planetary gear racing transmissions, racing countershaft transmissions are lighter than planetary gear racing transmissions. These countershaft racing transmissions are generally constant mesh transmissions having mechanical engagement devices, such as positive jaw clutches, that mechanically couple and uncouple components of the transmission to change the torque drive path through the transmission. These transmissions are sometimes referred to a xe2x80x9cclutchlessxe2x80x9d transmissions because they do not use clutch packs that are used by planetary gear transmissions to change gear ratios. Countershaft transmissions have been used in racecars that have engines that, while producing significant power, do not produce more power than can be used to drive the racecar. A primary objective for equipment used in the driveline of such cars, including transmissions, is to consume as little power as possible and thereby make as much power as possible available to drive the racecar. These transmissions have been developed for and are used by racecars that use clutches to obtain significant control over the application of power to the transmission and to avoid loss of power typically required to drive a torque converter. While these clutches and countershaft transmissions differ considerably in design and construction from clutches and transmissions used in conventional automotive applications, they nevertheless comprise a conventional combination of a friction clutch and countershaft transmission.
Racecars that do not have engines that create very high power have used, and continue to use, torque converter driven modified planetary gear transmissions that were originally constructed for conventional automotive applications. The engines used by many such cars have become sufficiently powerful that modified conventional transmissions fail unacceptably frequently. Recently, devices have been developed to drive a planetary gear racing transmission by a torque converter. Those devices are driven by a torque converter, have a brake mechanism to selectively and reliably withhold and apply power to the transmission, and have been developed specifically for use with racing planetary gear transmissions. One such device is disclosed by U.S. Pat. No. 5,090,528, which is incorporated herein by reference and is assigned to the assignee of the invention that is the subject of this application. Another such device is disclosed by U.S. Pat. No. 5,050,716. These devices, in combination with racing planetary gear transmissions, more nearly resemble the conventional combination of a torque converter and planetary gear transmission than does the combination of a clutch and planetary gear transmission.
The combination of a torque converter drive and a planetary gear racing transmission provides a reliable and durable driveline combination. However, many racecars that use that combination do not use engines that produce the highest power and therefor do not require transmissions having components as large and strong as those of racing planetary gear transmissions. In addition, even racecars for which total weight is not a critical consideration, the weight of planetary gear racing transmissions is a disadvantage because the significant weight of the transmission is at a fixed location in the racecar and thereby limits the amount of weight that can be distributed to increase performance and handling of the racecar. Further, because of the size and durability of their components, racing planetary gear transmissions are significantly expensive components of a racecar.
The need therefor exists for a driveline combination that includes a torque converter drive and a transmission that is lighter and less expensive than combinations that include a racing planetary gear transmission and that is durable and reliable. The need also exists for such a combination further including a driveline brake that can be closely controlled to reliably apply power from the racecar engine to the driveline.
In accordance with the present invention, the disadvantages of the driveline combination of a torque converter drive and a racing planetary gear transmission have been overcome. A combination is provided in which a torque converter drives a countershaft transmission. A releasable driveline brake may further be included in the combination to selectively withhold and then release power to the driveline of a racecar having the combination of this invention.
More particularly, the preferred combination of the present invention includes a torque converter to driveline coupler. That coupler includes a fluid pump adapted to provide fluid under pressure to a torque converter mounted to a flywheel that is mounted to an engine. The combination also includes a countershaft transmission. The coupler is adapted to engage an input shaft of the transmission and to drive the input shaft of the transmission from the torque converter. The countershaft transmission is preferably a constant mesh transmission.
Additionally, the torque converter to driveline coupler may include a fast-release brake that can prevent the coupler from driving the countershaft transmission when the engine is driving the torque converter.
Accordingly, an object of the present invention is to drive a countershaft transmission by a torque converter.
Another object of the present invention is to provide a combination of power transmission devices that is driven by a torque converter, allows manual changing of transmission ratios, and that consumes less power than previous torque converter drive and racing planetary gear transmission combinations.
Yet another object of the present invention is to provide a combination of power transmission components that is durable enough to withstand racing driveline loads and is less expensive than prior torque converter driven combinations.
These and other objects and advantages of the present invention, as well as details of the preferred embodiment thereof, will be more fully understood from the drawings and the following description.